Many people avoid drinking a post-workout protein shake because they believe consuming one is no more beneficial than waiting an indeterminate amount of time after training to consume a solid meal containing a high-quality protein source. In reality, the post-workout period presents a great opportunity to help achieve ideal protein distribution by consuming a modest dose of high-quality protein (1). This is important, because if you don’t take advantage of this opportunity, you can’t simply 'double down' on your protein intake in a later meal, as there is a cap on the quantity of dietary protein consumed in one meal which can contribute to muscle protein synthesis. Passing that cap entails the remaining circulating amino acids either being oxidized, being used to enhance ureagenesis (the excretion of excess nitrogen through urine), or being converted to glucose via gluconeogenesis (2). Although research shows consuming a quantity of protein above this cap at one meal has beneficial effects on whole-body protein balance, the resulting effects on muscle protein balance specifically are unclear (3). To quote protein metabolism researcher Dr. Stu Phillips: "[...] beyond what your body can immediately (or within a few short hours) use metabolically, large ‘doses’ of protein simply aren’t metabolically useful.” (4). As such, even if we assume there is no inherent benefit to consuming protein directly post-workout (an assumption not demonstrated in the relevant literature), it makes sense to do so for the sake of optimal protein distribution alone.

Admittedly, the above argument applies equally to the post-workout consumption of a solid food protein source as it does to the post-workout consumption of a protein shake. As such, it's important to consider the other benefits of consuming a protein shake after training, which can include far greater convenience and a lower monetary cost than consuming protein through solid foods.

In short, given 1) the known benefits of consuming a protein shake post-workout, 2) the possibility consuming a protein shake post-workout has as-yet-undiscovered inherent benefits, and 3) the absence of an overriding reason to generally avoid consuming a protein shake post-workout, we feel it solidly in the realm of evidence-based practice to recommend the consumption of a protein shake after training.